Inductive heating apparatus and method



Q @www OGL 27, 1942. l'v. w. SHERMAN ETAL 2,299,934

INDUCTIVE HEATING APPARATUS AND METHOD Filed Dec. 16. 1940 2 Sheets-Sheet l l N k\ K\ l "THUN/7%.

INVENTORS- Ker/7a fk5/.3cr 4f?,

ATTORNEYS 4 Oct 27, 1942. v. w. sl-u-:relmxaY E11-AL .2,299,934

INDUCTIVE HEATING A-PPARATUS AND METHOD l F11-ed Deo. 1e, 1940 z'sheetS-sheet 2 Patented Oct. 27, 1942 `INDUCTIVE HEATING APPARATUS AND METHO Vernon W. Sherman, Royal Oak, and Omer E. Bowlus, Highland Park, Mich., assignors to Chrysler Corporation, Highland Park, Mich., a

corporation of Delaware Application December 16, 1940, Serial No. 370,248

7 Claims.

This invention relates to an improved apparatus and method for directing the flux lines of a eld of an induction coil in predetermined paths. l

More particularly, the invention relates to an flux lines of the field of an induction heating coil may be distributed uniformly throughout substantially all portions of a piece of work or concentrated at selective parts of the work. l

One of the main objects of the invention is the provision of an apparatus and a method of this character which compensates for the distortion of the ux lines of an induction heating field which results from the counter magnetomotive f orce generated when a piece of work comprising electrical current conducting material is placed in a ux field.

Another object of the invention is the provision of inductive vheating apparatus of this kind which uniformly heats substantially all portions of Va piece of work without substantial loss of effective heating value of any portion of a flux eld.

Illustrative embodiments ofthe invention are shown in the accompanying drawings, in which:V

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1 improved apparatus and method by which the duction heating eld producing apparatus which is particularly suitable for use in connection with our invention.

Fig.` 6 is a diagrammatic view of an induction heating coil illustrating the courses of the flux lines of the field thereof in the absence of an electrical current conductive body.

Fig. 7 is a view similar to Fig. 6 but showing a piece of work comprising a conductive body in the field while illustrating in the lower portion of the figure the courses of the flux lines of the main and counter magnetomotive fields tend to follow and illustrating, in the upper portion of the figure, the resultant paths of the flux lines of the main eld.

Fig. 8 is a view similar to Fig. 6 but illustrating at the lower portion of the figure, the courses the flux lines of the main counter magnetomotive and compensating fields tend to follow and illustrating, in the upper portion of the figure, the resultant paths of the ux lines of the main field.

One inductive heating apparatus with which our invention may be used to particular advantage is illustrated in the form of a wire diagram in Fig.'5 in which is shown a circuit for producing and supplying to an inductive heating coil alternating current of ultra high frequency substantially of radio frequency order. This apparatus includes a thermionic tube I2 having a cathodel3, plate I4 and grid I5. The plate I4 is connected to a positive terminal of a high voltage source I6 by a conductor II in which is included a radio frequency choke I8. The negative terminal I9 of the high voltage source is connected by a conductor 20 to the cathode I3 and the cathode is grounded at 2|. The grid has a lead 22 connected to a conductor 23 which leads through a fixed condenser 24 to one terminal 25 of anl induction heating coil 26. The other terminal 2l of the heating coil 26 is connected by a conductor 28 with the plate I4 and the conductor II at 29. The conductor 28 includes a fixed condenser 30. A variable condenser 3I is shunted across the terminals 25 and 21 oi?y the heating coil. The cathode I3 may be variably connected to a selected turn of the coil 26 by a conductor 32. There is also included in the grid circuit a shunt connection from the conductor 20 to the grid lead 22 in which is included a radio frequency choke coil 33 and a -nxed resistance 34.

While the foregoing circuit is suitable for energizing an inductive heating coil with ultra high frequency alternating current, it will be obvious that any of a large number of circuits may be employed for this purpose in connection with applicants invention. It should also be understood that applicants invention may be used to advantage in connection with inductive heating apparatus supplied with current of any desired frequency characteristic.

In the form of the invention illustrated in Fig. l, there is provided within the interior of the coil 26 a support 35 preferably comprising di-electric material incapable of conducting electrical current The support 35 is of cylindrical shape and has an enlarged intermediate portion 36 at the extremities of which are mounted washers 3l,

also comprising di-electriccmaterial. The washer's 31 are predetermined in diameter to smoothly shape, dimensions and material of which they consist as to divert the portions of the ux lines of the field of the coil 26 adjacent the ends of the sleeve 38 outwardly in the same directions and to an extent substantially equal to the distortion of the portions of the ux lines in the vicinity of the intermediate part of the sleeve 38 as will be hereinafter more clearly described in connection with Figs. 6 to 8, inclusive.

In the form of the invention'illustrated in Fig. 2, there is disposed within the ,inductive heating coil 28 work supporting mechanism which comprises a central supporting bar 40 and spaced parallel supporting bars 4|. The central bar 40 is of rectangular cross section and adapted to fit snugly within the cylindrical piece of work 38 which illustrates only one of many forms of pieces of work the apparatus' is adapted to heat. Mounted on the upper and lower parallel bars 4| which, like the central bar 40, comprises di-electric material is a pair of ilux deecting elements 42. Each of the ux deecting elements 42 comprises a cylinder which is held in spaced relation to an extremity of the sleeve 38 by channelshaped clips 43 which are preferably formed integral with the sleeve-like body portions of the flux deflecting elements. The parallel bars 4| of the support mechanism are received in the chann els of the clips 43 as illustrated-in Fig. 3 so as to positively position the ux deflecting elements 42 with respect to the work.

- In the illustration shown in Fig. 2, the tubular flux deecting elements 42 are shown to be slightly'larger in diameter than the diameter of the sleeve 38. It is preferable that the iux de-` ecting elements 42 be at least as large in diameter as the work but, as hereinafter more clearly 'set forth, the outer dimensions of the ilux deectingelements may be varied by suitably proportioning the wall thickness and the character of the material of which these elements are formed. The flux deiiecting elements 42 are, like the corresponding elements 39 of Fig. 1, so predetermined and arranged as to compensate at the ends ofthe work 38 for the distortion of the ux lines of the field of the coil 26 at the intermediate part of the work piece which results from the countermagnetomotive force generated by the action of the eld on the work piece.

In Fig. 4 of the drawings is illustrated a modied form of the invention in which flux diverting elements embodying the invention are relied upon which comprises di-electric material and preferably centrally disposed within the coil 26. A ux "'deecting element 41 is mounted on the support l 46 and disposed adjacent the respectively/opposite side faces of the gear 44. The ux deilecting discs 41 are so constructed and arranged as to divert to the teeth 45 andadjacent peripheral portions of the gear the flux lines of the field of the coil 26 which normally tend to be distributed throughout the gear thus concentrating the action and effect in the portions of the gear which it is desired to harden or otherwise treat.

The operation of the flux deecting elements of each form of the invention is illustrated in Figs. 6, 7 and 8 in which an analysis of the action of the form of the invention illustratedin Fig. 2 is employed as an example. In Fig. 6 is illustrated the normal courses the ux lines 48 of the coil 26 take when passing only through air such as for example, in the absence of an electrical conductive body from the interior of the coil. The normal ux lines 48 extend substantially parallel to the axis of the coil 26 throughout a substantial portion oi its length. When a piece of work, as for example, the ferrous metal 38 is placed in the interior of the coil 26, there is a current induced in the ferrous metal which sets up a' counter magnetomotive field having flux lines extending in the paths illustrated by the dotted lines 49 as illustrated in the lower portion of Fig. 6. The mere presence of the work 38 in the field of the coil 26 causes the flux'lines of the latter to tend to concentrate in the metal of the work and to tend to flow in the courses illustrated by the dotted lines 50. The eifect of the flux lines 49 of the counter magnetomotive field in addition to the tendency of the flux lines to follow the body of the metal of the work, however, produces the resultant flux line courses 5| illustrated in the upper portion of Fig( 6. The flux lines 5| tend to thread through the end por- -tions of the work 38 but they are diverted outwardly fro'm the work by the counter magnetomotive force generated by the action of the eld of the coil 26 upon the work. This distortion of the flux lines of the field of the coil results in an uneven `distribution of ilux throughout the work and consequently produces non-uniform heating of the work. 'I'he directions in which the ux lines of the field of the coil 26 are diverted is dependent mainly upon the shape of the Work. Compensation for the foregoing ux line distortion may be made regardless of the shape of the work by appropriate construction and arrangement of the ilux diverting elements.

The operation of theA flux diverting elements A 42 of tubular shape upon the flux of a eld havto selectively direct and concentrate the flux lines L desired to heat in order to harden or otherwise treat the .metal of which these portions of the coil consist without excessively affecting the remaining portion of the coil. In this form of the ing a cylindrical piece of work 38 therein is illustrated in Fig. 8 in which the dotted lines 49 in the lower portion of the figure represent the paths the flux lines of the counter magnetomotived force tend to take, while the'dotted lines 66 represent the courses which the flux lines of the 'coil 26 tend to take as a result only of the presence of the work in the field of the coil. The presence of the flux diverting elements 42 in the eld oi the coil 26 results in the production of a third flux iield, the ux lines of which tend to follow the courses illustrated in dotted lines at 52 in the lower part of Fig. 8. This latter field is generated as a result of the current induced in the elements 42 which comprise electrical current conductive material. The resultant action invention. the gear 44 is mounted on a support 46 75 of the flux" lines 49 and 5,2 upon the iield of the coil is illustrated in the upper portion o! Fig. 8 in which the resultant paths of the flux lines are shown by dotted'lines 83. ing elements 42 which, as set forth above, may comprise diverse materials and shapes are so constructed and arranged with respect to the work Il as to divert the flux lines of the coil 2l which thread the end portions of the work outwardly substantially as far and substantially in the same direction a's the portions of the flux lines which register with the intermediate part of the work are diverted by the counter magnetomotive force generated by the action of the field upon the work.

In theforegoing manner, a compensation mayv be made in the vicinity of any selected portion of a piece of work for the counter magnetomotive force existing at any other portion of the work The flux deiiectf and the iiux lines of the inductive heating field may thus be selectively directed so as to uniformly heat all portions of a piece of work as illustrated inFig. 8 pr as to concentrate the heating action upon selected portions of a piece of work while shieldng other portions ofthe work in the manner illustrated in Fig. 4.

The foregoing flux" directing apparatus and method is particularly advantageous in connection with ultra high frequency inductive'heating processes for the reason that with ultra high frequency currents of the nature of radio frequency values, there is a tendencyto concentrate the heating action on the surface skin of the work when, as in the example illustrated in Fig. 6, the iiux lines are also concentrated at the ends or other isolated portions of a piece of work, the resulting non-uniform heating of the outer skin or surface of the metal is excessive and can be successfully controlled by diverting the fiux lines from such portions of the workin the manner illustrated.

Although but several specific embodiments of Athe invention have been herein shown and described, it will be understood that various changes in the size, shape and arrangement of parts may be made without departing from the spirit of the invention.

What is claimed is:-

l. Induction heating apparatus comprising means for producing a flux field. a support for positioning a piece of work to be threaded by the flux lines of said field, and flux diverting elements each comprising a closed, ringlike, mass of material of high electrical conductivity having a main body portion located within the longitudinal extremities of said field beyond the extremities of said piece o f work which are disposed transversely of the longitudinal axis of said field for producing, an induced counter magnetomotive force at a selected location to direct the flux lines of said field through and concentrate the same in selected portions of said work.

2. Induction heating apparatus comprising means for producing a nux iield including a coil membe a support comprising dielectric material extending axially of coil for positioning a piece of work to be threaded by the flux lines of said field, and flux defiecting elements comprising electrical current conductive material having a main body portion of generally annular cross sec.. tion each located between one of the longitudinal extremities ofA said field and that adjacent exthe portions 75.

of the flux lines of said field which register with said work generally parallel to the axis of said work.

3. Induction heating apparatus comprising means for producing an attenuating flux field of substantially radio frequency order, support means for positioning the walls of a cylindrical piece of work to be threaded in the general direction of the length of said work by flux lines of said field, and flux defiecting elements adjacent the extremities of said work comprising bodies of electrical current conductive material having tapered endportions extending thereinto and so constructed and arranged as to divert the flux lines of the portion of said field adjacent the ends of said work radially outwardly of s'aid cylindrical work piece substantially as far as the ux lines of thepart of said field adjacent the intermediate portion of said work piece are deiiected outwardly by the counter magnetomotive force generated by the action of said field on said work piece.

4. Induction heating apparatus comprising means for producing an alternating flux field of substantially radio frequency order, support means for positioning the walls of a' cylindrical piece of work to be threaded in the general direction of the length of said work by flux lines of said field, and flux defiecting elements adjacent the extremities of said work comprising cylindrical bodies of electrical current conductive material having a diameter at least as large as that of said work piece and arranged in spaced substantially concentric relationship with respect to the extremities of said work piece for compensating, at the end portions of said work piece, for the distortion of the flux lines of said field caused at the intermediate part of said work piece by the counter magnetomotive force generated by the action of said field on said work piece. f

5. Apparatus for selectively inductively heating the teeth and adjacent peripheral portions of a gear comprising means for producing an alternating flux field, a support for positioning a gear in said field with its radial planes disposed subconductive material and arranged adjacent opposite side faces of said gear for diverting to the teeth and adjacent peripheral portions of said gear the flux lines of said field which are normally distributed throughout the gear.

6. Induction heating apparatus comprising means for producing a flux field, a support for positioning a piece of work to be threaded by the flux lines of said field, and a flux diverting element comprising metal of high electrical conductivity for producing an induced counter magnetomotive'force at a selected location, said element having a closed ring body portion located between one longitudinal extremity of said field and a corresponding extremity of said piece of work and being so constructed and arranged as to repel certain of the iiux lines of said eld threading said extremity to substantially the same extent as the flux lines in the vicinity of another portion of said piece of work are repelled by the induced counter magnetomotive force generated by the action of said field on said latter portion of said work.

'1. In inductively heating articles, the method of directing the flux lines of an inductive heating field which comprises repelling by an induced counter magnetomotive force the portions of the ux lines adjacent opposite end portions of a the path of said ux eld immediately in advance piece of work in the same direction and substanof the opposite ends of said work and between the tially as far as the portions of said iluX lines adlatter and the longitudinal extremities of said jacent intermediate portions of said work are reeld. pelled by the counter magnetomotive force gen- 5f 'VERNONW. SHERMAN.

erated by the action of said field on said work by OMER E. BOWLUS, placing electrical current conductive material in 

